1. Field of the Invention
The present invention is directed to an x-ray diffractometer for conducting a spectral analysis of a specimen.
2. Description of the Prior Art
X-ray spectrometers serve the purpose of non-destructive analysis of solid, powdered and liquid specimens. Powder x-ray diffractometers have achieved wide usage among devices of this type, because they have a relatively simple structure and are versatilely employable. With such a device, unknown substances and substance mixtures can be identified, their lattice structure can be defined and conclusions about their crystallization state can be made from the diffraction diagrams acquired (see, for example, Siemens Forschungs- und Entwicklungsberichte, Vol. 14 (1985) No. 4, pages 167-176).
Powder diffractometers predominately employ focusing beam arrangements that guarantee a high exploitation of the x-ray beam irradiating the specimen. In order to obtain a beneficial contrast of diffraction maxima relative to background, monochromator crystals are often utilized at the primary side or secondary side. The secondary monochromators are usually composed of bent graphite mosaic crystals and have the advantage that they are capable of separating the usable diffraction radiation from the fluorescent radiation which is unavoidably produced in the specimen.
The mensuration technology of radiography was decisively enriched in the 1980's by the employment of position sensitive detectors. These detectors act as a plurality of individual counters and thus allow significantly faster data collection. As a consequence of the increases in the measuring speed by more than a factor 100 accompanying this, advance "snapshots" of chronologically variable conditions (solid state reactions, phase conversions) are capable of being made in the specimen.
Position sensitive detectors have especially proven useful in combination with monochromators on the primary side. Strictly focusing primary monochromators of high-perfection single crystals (germanium, silicon, quartz) are preferred in such combinations because these crystals are capable of resolving the K.alpha..sub.1 -K.alpha..sub.2 doublets that are problematical for the interpretation of the diffraction diagrams. Diagrams having only K.alpha..sub.1 reflexes are therefore obtained, whereby the intensity loss of the primary x-ray caused by the monochromator is more than compensated by the employment of the position sensitive detector.
Compared to conventional methods of x-ray analysis, a technique referred to as total reflection x-ray fluorescence analysis (TXRF) has a high surface sensitivity, since the exciting radiation is incident on the specimen under examination at an extremely small angle .alpha.&lt;0.5.degree., and thus penetrates only a few nanometers into the specimen. The TXRF method is therefore particularly suited for the identification of the chemical composition of thin layers and surfaces. A TXRF measuring apparatus is described in European Application 0 456 897. Instead of having a monochromator of the primary side, this measuring instrument has a multi-layer mirror that deflects the radiation generated in an x-ray tube in the direction toward the specimen under examination without a greater loss in intensity.